At present, comparing the organic electroluminescent display device (OLED) with the traditional liquid crystal display device (LCD), because of having the features such as fast response, large color field, extremely thin, realization of flexibility, and the like, OLED has gradually become the mainstream of the display field.
The basic structure of an OLED display device comprises a base substrate, an organic electroluminescent element formed on the base substrate; wherein each organic electroluminescent element comprises a cathode and an anode provided opposite to each other, and an organic light emitting layer between the cathode and the anode. The light emission of an OLED display device is achieved by applying a voltage between the anode and the cathode, wherein holes in the anode and electrons in the cathode recombine in the organic light emitting layer to form excitons, the excitons in excited state transfer into the ground state, so as to excite the organic light emitting material in the organic light emitting layer to emit light. The organic light emitting material may be divided into two types according to the light emitting mechanism: one is composed of a fluorescence material emitting light by singlet excitons, and the other is composed of a phosphorescent material emitting light by triplet excitons.
In an OLED display device, in order to improve the light emitting efficiency and the stability of the formed OLED, the organic light emitting layer may comprise film layers such as a hole injection layer, a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injection layer, and the like formed from different organic materials, respectively. In order to improve the light emitting efficiency of the organic light emitting layer, a doping material having higher quantum yield than that of the host material may be doped into the host material of the light emitting layer. This is because the excitons in excited state have the tendency of transferring the energy thereof to the material having a smaller band gap in the material near the recombination portion. Therefore, the doping material is selected from the materials having a higher quantum yield and a smaller band gap (larger wavelength) comparing with those of the host material; otherwise, the energy of the excitons in excited state will transfer to the host material having a lower quantum yield, so as to produce weak emission or no emission.
In order to improve the light emitting efficiency and the light emitting brightness of the organic light emitting layer in an OLED display device, it has become a problem to be solved by a person skilled in the art to provide a stable and highly efficient organic light emitting material to be applied into the organic light emitting layer of the OLED display device.